According to initial measurements by the Greek Geodynamic Institute in Athens, the quake had a magnitude of 5.8 and struck at 9.12am local time on Friday.

The epicentre of the quake was about 20km below the seabed off the west coast of the Peloponnese peninsula near the islet of Stamfani, also known as Strofades. It was preceded by a smaller quake of magnitude 4.1.

Greece's Civil Defence organisation did not initially say whether there were any casualties or damage to buildings. A tsunami warning was not issued.

"We felt the tremors very strongly," a resident of the nearby Olympia region told dpa. "Everyone here is on the streets," he added.

Reporters from local media reported that many schools had been evacuated.

The quake was felt throughout western Greece, on the tourist island of Zakynthos and as far away as Athens, around 300km away.

The deepest point of the Mediterranean Sea is located between western Greece and Sicily in Italy, with a depth of over 5000 metres.

The African and European tectonic plates meet in this region, which is consequently prone to strong earthquakes.

Australian Associated Press